1. Field of the Invention
This invention relates generally to magnetic recording heads, particularly to perpendicular recording heads that produce their recording magnetic fields perpendicularly to the recording medium
2. Description of the Related Art
The increasing need for high recording area densities (up to 500 Gb/in2) is making the perpendicular magnetic recording head (PMR head) a replacement of choice for the longitudinal magnetic recording head (LMR head).
By means of fringing magnetic fields that extend between two emerging pole pieces, longitudinal recording heads form small magnetic domains within the surface plane of the magnetic medium (hard disk). As recorded area densities increase, these domains must correspondingly decrease in size, eventually permitting destabilizing thermal effects to become stronger than the magnetic interactions that tend to stabilize the domain formations. This occurrence is the so-called superparamagnetic limit. Recording media that accept perpendicular magnetic recording, allow domain structures to be formed within a magnetic layer, perpendicular to the disk surface, while a soft magnetic underlayer (SUL) formed beneath the magnetic layer acts as a stabilizing influence on these perpendicular domain structures. Thus, a magnetic recording head that produces a field capable of forming domains perpendicular to a disk surface, when used in conjunction with such perpendicular recording media, is able to produce a stable recording with a much higher area density than is possible using standard longitudinal recording. In this regard, Yoda et al. (U.S. Pat. No. 6,912,769) teaches a thin film magnetic head for perpendicular recording in which the main magnetic pole tip protrudes through an aperture formed within a thin film.
A significant problem with magnetic pole structures that are currently used to produce perpendicular fields, is that the fields tend to exhibit significant lateral fringing, thereby producing unwanted side-writing (writing in adjacent tracks). This problem is much more evident in the perpendicular writing head than in the longitudinal writing head, even when the perpendicular head is shielded laterally to contain the fringing fields.
Among the efforts in the prior art to address the adverse effects of field fringing is the shielded head of Hsu et al. (US Patent Application Publication US2005/0068678) that uses side shields connected to a trailing shield by ferromagnetic studs. By locating the studs behind the ABS of the head, the return flux flow does not impinge on the disk itself. Yazawa et al. (US Patent Application Publication US 2005/0057852) teaches a perpendicular magnetic writing pole that includes a shield layer conformally formed over the pole. Thus, there is a single piece shield that covers top and side surfaces of the pole. Such integral formation allows the formation of a large shield which, it is suggested, is better able to absorb the return flux of the recording head. Batra et al. (US Patent Application Publication US 2002/0071208) teaches a perpendicular magnetic recording head in which the write pole is structured so that its return pole is itself formed surrounding the main pole. Thus it is the pole shape that eliminates a large degree of undesirable field fringing. The pole can, in addition, be surrounded by side shields to further reduce the effects of fringing. Kimura et al. (US Patent Application Publication US 2005/0162778) describes a method of forming the track restriction region of the main pole of a perpendicular recording head using an ion milling process. There is no particular mention of the formation of shields around the pole.
The present inventors, in related application HT 05-039, fully incorporated herein by reference, provided a method of forming a three-way side shielded head (top and side shields) that significantly reduced side fringing and, as a result, allowed the formation of a larger pole, while providing the same degree of track resolution and protection from side overwriting. As an aspect of that invention, the side shields themselves are used to form the pole tip, using a trench formed within the side shields to provide a self-aligned method of shaping the pole tip in an advantageous manner. More recently, further study of the shielded head design cited above indicated that it was possible to improve on the performance of that design, particularly with respect to further reduction of field fringing and an improvement in the tightness and definition of the field flux at the recording surface. Reduction of field fringing is of great importance in eliminating the problem of overwriting, in which writing on one track affects what has already been written on adjacent tracks. Essentially, the reasons for the improvement can be stated as follows. If the pole tip of the writer was completely unshielded, there would be a high flux at the surface of the medium, but the spreading of the flux would produce poor resolution and adjacent track overwrite. In the design of HT 05-039, the shield substantially covered the entire sides of the pole tip, thereby producing good overwrite performance, but low flux. It will be the object of the present invention to strike the middle ground, whereby the vertical extension of the shields will be less than that of HT 05-039, thereby providing a gain in spatial resolution, while not sacrificing the flux strength at the recording medium.